PURPOSE: To perform positioning in a short time with a high degree of accuracy by deforming a resilint deformable member between first and second nuts in accordance with an external signal which is produced in response to the movement of a movable member, so that different pressurizing forces and/or directions may be exerted to the nuts.

CONSTITUTION: A subnut 6 is attached to a main nut 4 provided on movable stage 3, through the intermediary of a piezoelectric actuator 8, a pressure sensor 9 and a leaf spring 5, and is screwed onto a feed screw 2. A control circuit 20 receives signals from a pressure sensor 9 and an accelerometer 10, and computes precise positioning data of the movable stage 3 so as to drive a servomotor 1. Further, the control circuit 20 delivers data for controlling at least one of the degree of pressing force between both nuts 4, 6 and the direction thereof in accordance with an inertia force during deceleration, to the acruator 8. Accordingly, it is possible to position the movable stage 3 in a short time with a high degree of accuracy.